Commercial metal doors are typically comprised of vertical stiles interconnected by top and bottom rails. Optionally an intermediate rail can be used to provide additional structural rigidity. Infill panels such as glass lites are set in the rectangular openings defined by the stiles and rails.
The stiles and rails are typically comprised of hollow frame members of aluminum or other suitable material. One problem associated with conventional metal commercial doors concerns the joints between stiles and rails. Commercial doors are typically subject to heavy use and abuse, which cause the door to be twisted and racked. This twisting and racking exerts substantial force on the corner joints. While many prior art commercial doors have corner joints which can withstand these forces, manufacture of the corner joint components is expensive, and the doors can be time-consuming and labor-intensive to assemble. Prior art efforts to provide a corner joint design with lower cost components and which can be assembled more quickly and with less labor have resulted in corner joints which are subject to failure from the twisting and racking which result from heavy use.
Thus there is a need for an improved commercial metal door having corner joints which employ less expensive components, can be assembled quickly and with a minimum of labor, and yet will exhibit structural integrity to withstand the rigors of heavy use.
Corner joints for prior art commercial doors have typically fallen into one of two categories. In a first category, shear blocks are anchored to the glazing face of each door stile with threaded fasteners. The open ends of the rails are then advanced over the shear blocks, and screws are inserted through a glazing face of the rails and into the respective shear blocks. Tightening the screws draws the rails snugly against each stile and anchors the rails to the stiles. While this arrangement makes for a sturdy joint, the shear blocks must be designed to withstand heavy forces, as the shear block provides the sole structural connection between the stiles and the rails. In addition, the requirement that the shear block be screwed to the stile and that the rail be screwed to the shear block makes assembly labor-intensive.
The second category consists of tie-rod doors. A clip is mounted within a track on the glazing face of the stile. The block has a circular bore which overlies a similar bore in the glazing face of the stile. A threaded rod extends longitudinally through each rail and project from each end. The projecting ends of the tie rod are inserted through the clips and into the stiles. The clip fits snugly within the open end of the rail. Threaded fasteners within the stiles are threaded onto the ends of each rod to draw the rail against the stiles and to connect the rail to the stiles. The engagement of the clip within its track prevents the clip from rotating. In turn, the clip fits snugly within the open end of the rail to prevent the rail from turning.
Since the tie-rod, and not the clip, is the primary structural connection between the rail and the stiles, and since the only purpose of the clip is to prevent the rail from twisting, the clip need not exhibit the structural strength of a shear block and can thus be fabricated from lighter weight, less expensive materials. In addition, since the track holds the clip in place without the need for screwing the clip to the door stile, and since the threaded rod holds the rail against the door stile without the need for screwing the rail to a shear block, installation requires less labor.
However, prior art tie-rod doors have been found to provide joints having less than optimal structural integrity. As the door is twisted or racked, causing the rail to exert a rotational force against the clip, the corners of the clip impart these forces against the outer wall of the stile. Because these forces are concentrated on a relatively small area of the wall of the stile, and because the outer walls of the stile are not designed to withstand such concentrated forces, the stile over time will begin to deform. The result is that the clip has more "play" to rotate within its track, and the rail in turn begins to exhibit a certain degree of rotation with respect to the stile. As the joint loses its integrity, the door frame deforms as it is subjected to twisting and racking.
Thus there is a need for an improved corner joint for tie-rod doors which exhibits improved resistance to twisting.